On-Net Surveillance Systems, Inc.
NetDVMS 6.5e
Daylight Saving Time
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Daylight Saving Time
Daylight saving time (DST, also known as summer time) is the practice of advancing clocks in order for evenings to
have more daylight and mornings to have less. Typically, clocks are adjusted forward one hour sometime during the
spring season and adjusted backward sometime during the fall season, hence the saying
spring forward, fall back
.
Note that use of DST varies between countries/regions.
Clocks are adjusted forward when DST starts
When working with a surveillance system, which is inherently time-sensitive, it is important to know how the system
handles DST.
Spring: Switch from Standard Time to DST
The change from standard time to DST is not much of an issue since you jump one hour forward. Typically, the clock
jumps forward from 02:00 standard time to 03:00 DST, and the day thus has 23 hours. In that case, there is simply no
data between 02:00 and 03:00 in the morning since that hour, for that day, did not exist.
Fall: Switch from DST to Standard Time
When you switch from DST to standard time in the fall, you jump one hour back. Typically, the clock jumps backward
from 02:00 DST to 01:00 standard time, repeating that hour, and the day thus has 25 hours. In that case, you will
reach 01:59:59, then immediately revert back to 01:00:00. If the system did not react, it would essentially re-record
that hour, so the first instance of, for example, 01:30 would be overwritten by the second instance of 01:30.
Because of this, NetDVMS will forcefully
archive
the current video in the event that the system time changes by more
than five minutes. The first instance of the 01:00 hour will not be viewable directly from access clients (
NetGuard
and
NetGuard-EVS
). However, the data is recorded and safe, and it can be browsed using the
Viewer
application by
opening the archived database directly.
